Sartorius DCU 3, Operator'S Handbook Manual

Page: 26 / 150

Operators Handbook DCU3 – System
5., Main Function „Calibration“
BAEDCU3 - Rev. 4.6 - 0504 5 - 4
5.3 pO
2
- Calibration
The pO
2
- electrode is calibrated in terms of percentage oxygen saturation, „% pO
2
“. The calibration is
a two-position calibration. In a fermentor the oxygen-free culture medium is the zero reference and the
medium saturated with oxygen is the „100 % pO
2
“ - reference. The pO
2
-electrode is calibrated while it
is installed in the culture vessel and after the sterilization. Therefore the calibration considers possible
interferences resulting from heat impact or chemical effects during sterilization.
In in-situ sterilized culture vessels you can enter the current of the electrode measured at
the end of the sterilization cycle as zero reference of the electrode.
If it is impossible to measure the zero current before air is introduced, you can connect a ni-
trogen source to the air input and gas the vessel with oxygen-free nitrogen to replace the
oxygen dissolved in the medium.
The slope can be measured after gassing the medium with air (or gas mixtures containing
oxygen) at the operating conditions intended for the process. During the process the DCU -
system calculates the actual pO
2
considering the zero reference, slope and temperature.
The structure of the operating display for calibration of the pO
2
-electrode is nearly the same as for the
pH-calibration. See the display on your DCU - system for details or refer to the pH - calibration display.
The display shows the „pO
2
-saturation“ (% pO
2
), the actually measured electrode current, the actual
temperature and the zero and slope current together with the calibration conditions. This, in addition,
allows a simple function control of the pO
2
-electrode.
5.3.1 Calibration
5.3.1.1 Zero Calibration
1. Before starting the zero calibration: sterilize the vessel (i.e. run the sterilization cycle at in-
situ sterilizable fermentors) or
– connect a supply of oxygen-free nitrogen and gas the medium until any dissolved oxygen
is exhausted.
2. Inititate the calibration of the electrode´s zero via „Start ZERO Calibration“. Follow the in-
structions given in the calibration menu.
If the displayed zero current (ZERO: ....) is not in the range of 0 ... +10 nA, the pO
2
-
electrode must be checked and serviced.
5.3.1.2 Calibration of Slope
1. Gas the medium with air (or the intended gas mixture containing oxygen) at the conditions
(flow rate, pressure, temperature) intended for optimum oxygen supply. A constant elec-
trode current will indicate that the medium is saturated with oxygen.
2. Inititate the slope calibration via „Start SLOPE Calibration“ and follow the instructions given
in the calibration menu.
If the measured current remains below 30 nA, the electrode must be checked and serviced.
5.3.2 Special Notes
At a first use or at any time the pO
2
-electrode has been disconnected from the amplifier for
more than 5 ... 10 min. it must be polarized. This polarization takes at least 6 h (the time will
be shorter, if the electrode is disconnected for only a few minutes). See information in the
Operating Manual of the fermentor or in the documentation delivered with the electrode.
If necessary the „Zero“ and „Slope“ can be entered manually into the corresponding fields.